Plants that repel spiders are referred to as "companion plants." They are so-called because of their properties to repel spiders from the soil, leaves and flowers of plants while simultaneously serving their vegetation purpose. Some dispel the repellent properties of companion plants as "unproven" or "old wives tales." Yet some gardeners swear by their properties to repel spiders from their prized plantings. Give them a try. The risks of plantings are minimal, and you can judge their repellent properties for yourself.
Onion and Garlic
Use onion and garlic for companion spider-repelling plantings to protect vegetables from red spiders and spider mites. Gardens use onion and garlic as a repellent to protect vegetables such as cabbage, cauliflower, broccoli, beets, tomato and lettuce, and to protect fruit plantings such as strawberries. However, there is a caution in using onions near peas and beans. Planting onions nearby peas and beans is said to inhibit their growth.
Horse chestnuts are commonly referred to as "conkers." Many consider conkers to be a natural repellent for spiders. Those who believe in their repellent properties to repel indoor spider infestations primarily use the chestnuts, placing them near doors and windowsills to keep spiders from invading rooms inside of the home.
Osage Hedge Balls
Osage hedge balls have an appearance that alone could frighten a spider away. They are cauliflower-looking green fruits with an odd, oval shape. They also have interesting names that could repel anything from a human to an insect, such as the spiders. Common names include monkey balls, brain fruit and green brain. For decades, once the hedge balls fall from the tree in early fall, people have placed them inside their homes as a natural repellent for spiders, even before "organic" was a well-known term. If you're interested in trying this plant as a repellent and you don't have an Osage tree, don't worry. You can order fruits online, look for them at a farmer's market or ask your grocer to order them for you.
Growing cilantro can reap triple benefits. You'll have a nice spice to add when making fresh salsa and Mexican dishes. And if you leave plants to seed after flowering, the seeds will become coriander -- another ideal spice for cooking. Let the coriander seeds "do their thing" and dry and deposit into the soil. The dried seeds will repel spider mites from your garden.